This invention relates to an extrusion machine with a spiral conveyor for forming concrete or other modable materials, and by the addition of a cutting and core-plugging mechanism, being able to produce automatically and directly single (narrow and wide) slabs of the required size and specification.
Prior technology of extrusion machines for producing prestressed concrete cored slabs, and the present invention of an extrusion machine for producing prestressed concrete cored single slabs (including wide slab extrusion machine and narrow slab extrusion machine) have both been used for the production of prestressed concrete cored components. By integrating the delivery, extrusion and vibration processes, concrete slab can be produced requiring no timber, economizing cement and steel consumption, rendering high strength and sound quality as well as raising the working efficiency by 4-6 times in comparison with any other prior methods. The development of extrusion machine creates a requisite for the realization of factory-processing (i.e. so called housing factory) in building construction.
For nearly two decades, many interested parties both in China and abroad, have spent substantial man-power, material and financial resources in actively undertaking the research of an extrusion machine. In the early 1960's, Canada was the first to successfully complete the research in the type of extrusion machine that utilitizes the spiral conveyor for forming concrete components. Since then, the United States, Britain and the Federal Republic of Germany have also achieved successively in their respective researches of the extrusion machines having various characteristics, for which several patents were granted, including those published such as, Canada Patent No. 985191 (1974), U.S. Pat. No. 4,273,522 (1979), European Patent No. 080333 (1982), etc, Nevertheless, there are disadvantages in all of these machines, including: (1) a hopper is incorporated in the machine, that causes vibration to the concrete aggregates and their ultimate agglomeration, and also increase in the weight of machine; (2) specially constructed casting beds are needed, with each being able to produce only one type of slab corresponding in size and specification; (3) a worm gear, worm shaft and chain transmission system is being used resulting in low efficiency of the machine (below 50%); and (4) the high cost of a spiral conveyor which poses a poor economic effect.
In 1977, Ren Deguo et al, of China succeeded in their research for a new type of extrusion machine which overcomes all of the above-mentioned disadvantages. The new machine is provided with the following characteristics: the hopper is separated from the main machine and supported by four posts directly in contact with the ground, with rollers employed for pushing the hopper forward, thus eliminating not only the agglomeration of concrete but also the need of providing any crushing mechanism (or feeding mechanism); by the use of restraining devices in front and at intermediate parts for positioning and guiding of reinforcing steel, and together with the elimination of special casting beds by the substitution of flat concrete ground for production, site utilization rate is upgraded and construction cost is lowered; by using the fully-sealed transmission mechanism with all slanting multi-level deceleration and multi-axial output, efficiency rate of the machine can be greatly upgraded (up to 86%) thus reducing the energy consumption; and the use of a new type of spiral conveyor which is high in strength and well-resistant to wear, with each piece of the conveyor having a performance capacity of 20,000 meters in travelling-distance.
In spite of its many advantages, this new type of extrusion machine is similar to other extrusion machines in that the cored slabs produced are all elongated or continuous plates, whereas the actually required cored slabs are rectangular ones having certain specified lengths. The common practice of dividing the elongated slabs is to cut them into sections corresponding to the desired sizes. Known methods of cutting comprise rigid cutting and soft cutting. Rigid cutting is carried out when concrete reaches its ultimate strength of 70%, and by using a saw-blade formed of welded diamond chips, concrete and the reinforcing steel are cut simultaneously. The disadvantages of this method are: (1) high in cost, (2) without spare of swing-back steel on either ends of the slab, and (3) the susceptibility to cracks due to contraction during the hardening of the elongated slab, resulting in the increase of wastes. Soft cutting, on the other hand, is carried out when the cored slab has just been formed, and with manual operation (by raking or sawing) to divide a part of the concrete component into required sections (reinforcing steel being kept uncut temporarily). The disadvantages of this method are the high consumption of time and labour, the heavy manual work, as well as the nonavailability of the degree of roughness at the ends and discrepancy in size length. Therefore, both methods are not ideal for application.
The width of cored slabs currently in use is basically equal to or smaller than 1.2 meters. By arranging these narrow slabs to form "wide slab" will have the disadvantages of: (1) the discrepancies in prestressing controls existing in different slabs will form a kind of uneven ceiling; (2) grouting of seams is relatively difficult and the appearance of cracks is more common; (3) the efficiencies in transportation and construction are rather low. Large size slabs currently being used in China may overcome certain disadvantages as the above-metioned, but still have the defficiencies of being heavy in weight, high consumption of concrete and steel, as well as low performance in sound and thermal insulation. Thus, the solution of the problem of producing large size cored slabs with a high efficiency machine has become an urgent need to the present day construction industry, and also the one of practical significance.